subscription: remove hard-coded white background

subscription: remove hard-coded white background

setting the background color in js code adds that property as a style
attribute to the element. that makes it hard to alter later via css
and makes it hard to dynamically change the color e.g. if we want to
add different themes. the background color for this element is white
already anyway, so just remove them here.

Signed-off-by: Stefan Sterz <s.sterz@proxmox.com>
Reviewed-by: Dominik Csapak <d.csapak@proxmox.com>
Tested-by:  Dominik Csapak <d.csapak@proxmox.com>